The present invention relates to a selectively light-absorptive material, a coating composition containing the material, and a filter manufactured using the coating composition, which are for use in color displays with enhanced color purity and contrast.
Color displays have been extensively applied to television, computer monitors, video game machines and the like. Cathode ray tubes (CRTs), which are a kind of display adopted for almost all of these applications, are based on the principle of energy conversion, i.e., from motion energy to light energy, in which electrons emitted from an electron gun hit phosphors of a screen and excites the phosphors. Since light emitted from the phosphors belongs to the visible range, CRTs can be used for displays such as common televisions or computer monitors. CRTs are able to display the full range of colors with the three principal colors: red (R), green (G) and blue (B).
FIGS. 1 and 2 show the emission spectra for CRTs and plasma display panels (PDPs), respectively. As shown in FIGS. 1 and 2, a considerable amount of light is emitted from the peripheral region adjacent to the three main R, G and B peaks, so that color purity is deteriorated and color reproduction range is limited. FIG. 1 shows the typical emission spectrum of a CRT. As shown in FIG. 1, typically a green-color emission spectrum is wide and tends to be close to the yellow range. Thus, as for CRTs, red and blue color emission can be achieved with high-color purity. However, as for green color emission, yellowish green light, rather than pure green light, is emitted.
On the other hand, reflection of ambient light from the surface of a display causes eye strain to viewers, and degrades the contrast of the display when the display is exposed to bright ambient light. Reflection of light, which occurs in displays, involves the reflection of ambient light from a screen, for example, a glass panel, and from phosphors arranged inside the screen. To reduce such reflection of light, research has been conducted. For example, U.S. Pat. No. 4,989,953 relates to a reduction of reflected light. However, this disclosure is limited only to reducing glare caused by reflection of external light in a monochromic monitor.
As a trial for reducing the reflection of light in color displays, a neutral density (ND) filter or an attenuator has been adopted. The ND filter, which is manufactured by coating an appropriate medium with a silver or graphite colloid suspension and attaching the medium to the surface of the monitor, improves contrast by transmitting only a portion of light regardless of the wavelength. However, the ND filter lowers brightness.
As another technique for reducing the reflection of light in color displays, an antireflection coating may accompany the ND filter. This combination technique can decrease the reflection of ambient light from phosphors, and the reflection of light from the surface of the display panel. This method is unsuitable for improving the brightness and color purity.
To improve both color purity and contrast, and to minimize a reduction in brightness, a method of transmitting only light of three principal color regions and blocking light of the other regions has been suggested. Compared to the ND filter, this method is able to block ambient light and fully transmit light generated in a display, and thus the reduction in brightness can be minimized with increased contrast. In addition, various colors other than the three principal colors, which are generated in the display, are effectively blocked, thereby improving color purity and expanding color reproduction range.
U.S. Pat. Nos. 4,288,250, 4,520,115 and 4,245,242 teach the use of a colored glass as a material for the front panel of a display, or as a filter, which contains a metal oxide including neodymium oxide. These disclosures allow the passage of light of the three principal color range emitted in the display and limit the transmission of light outside this range, so that a reduction in brightness is prevented and reflectivity of ambient light is lowered with improved color purity. However, the manufacture of the colored glass is complicated and the manufacturing cost increases. Thus, the methods are economically unfavorable.
JP Publication No. sho 44-5091, and JP Laid-open Publication Nos. sho 59-217705, hei 4-106150, hei 6-88007 and hei 10-120860 disclose the improvement in display properties of a color display using a colored plastic manufactured by dispersing or dissolving a neodymium oxide or an organic neodymium compound in plastic resin. However, there are difficulties in the dispersing or dissolving process of these methods. Furthermore, the plastic material changes into a yellowish color and the display properties gradually deteriorate with time.
JP Laid-open Publication No. hei 2-210480 and U.S. Pat. No. 5,200,667 suggest a filter for color displays, which contains a pigment and a plastic resin material as major components. However, the pigment suggested by the disclosures has a wide absorption bandwidth and a low light selectivity. Thus, the color purity cannot be improved. U.S. Pat. No. 5,834,122 discloses a band pass filter for displays with improved light selectivity, which contains a highly color-selective pigment. However, because pigments absorbing light in the range between green and red colors and light in the range between blue and green colors have weak durability, the method is unpractical.
Use of another type of display, the plasma display panels (PDPs), is gradually increasing. As for PDPs, a space enclosed by barrier walls made of glass is filled with inert gases including helium (He), neon (Ne), argon (Ar) or xenon (Xe), or a mixture of these gases, and the gases filling the space are ionized to create plasma by applying a high voltage. At this time, ultraviolet (UV) rays are emitted to excite phosphors. PDPs provide a wider viewing angle, and are easier to enlarge compared to other displays. Thus, PDPs as a thin-type luminescent display have been considered as highly potential display devices for high-definition televisions.
Now, such PDPs are under development by many display manufacturers. However, their brightness is low and the reflection of light from the surface of the phosphor is serious. Furthermore, the filling gas, He, emits light with an orange color, and thus the color purity is poor compared to CRTs.
FIG. 2 shows the emission spectrum of PDPs. Compared to the emission spectrum of CRTs shown in FIG. 1, the emission peak of green tends to have a slightly shorter wavelength, and the emission peak of blue tends to have a longer wavelength. Also, a strong emission peak of red is shown near 590 nm. This emission peak of red near 590 nm originates from the use of Ne as an inert gas. Thus, it is difficult to display pure red color. As for blue color, greenish blue light, rather than pure blue light, is displayed.
In terms of various uses of CRTs and PDPs and potential uses thereof, there is a need for an apparatus and mechanism capable of lowering the reflection from the surface of a display, and improving color purity and contrast without considerable loss in brightness and distinctness.
To satisfy these requirements, the present inventors have actively carried out research so as to improve the color purity and contrast by absorbing light reflection in a color display. As a result, it has been found that use of a light absorbing material capable of absorbing light between the green and UV regions, between the green and red regions, and between the red and infrared regions, from the emission spectrum, as a filter for color displays, can improve color purity and contrast in the color display.
A first object of the present invention is to provide a selectively light-absorptive material for color displays, which is able to absorb light reflected in a color display and light of the intermediate colors exclusive of the three principal colors, with improved color purity and contrast in the color display.
A second object of the present invention is to provide a selectively light-absorptive coating composition containing the light-absorptive material.
A third object of the present invention is to provide a selectively light-absorptive filter including the selectively light-absorptive material.
The first object of the present invention is achieved by a selectively light-absorptive material for a color display, comprising a tetrazaporphyrine derivative having formula (1) 
where R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from the group consisting of hydrogen; an unsubstituted phenyl group, an alkyl group of 1 to 8 carbon atoms; an alkoxy group of 1 to 8 carbon atoms; a nitro group; halogen atoms; a halide; a cyano group; an alkylamino group of 1 to 8 carbon atoms; an aminoalkyl group of 1 to 8 carbon atoms; and a phenyl group having a substitutent selected from an alkyl group of 1 to 8 carbon atoms, an alkoxy group of 1 to 8 carbon atoms, a nitro group, halogen atoms, a halide, an alkylamino group of 1 to 8 carbon atoms, an aminoalkyl group of 1 to 8 carbon atoms and a cyano group, or two neighboring substituents among R1, R2, R3, R4, R5, R6, R7 and R8 are fused and substituted with 1 to 3 aromatic cyclic compounds having formula (2a) through (2g), and unsubstituted groups among R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from the group consisting of hydrogen, an alkyl group of 1 to 8 carbon atoms, an alkoxy group of 1 to 8 carbon atoms, an allyl group, halogen atoms, a halide, a cyano group and a nitro group 
where Rxe2x80x2, Rxe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x3xe2x80x3xe2x80x2 are independently selected from the group consisting of hydrogen, an alkyl group of 1 to 8 carbon atoms, an alkoxy group of 1 to 8 carbon atoms, an allyl group, a cyano group and a nitro group; X is halogen atoms or alkyl sulfonate of 1 to 8 carbon atoms; Y is an alkyl or allyl group of 1 to 8 carbon atoms; and dashed lines indicate a portion coupled with the pyrrole group of formula (1).
In another embodiment, a selectively-light absorptive material for a color display, may comprise a tetrazaporphyrine derivative having formula (3) 
where R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from the group consisting of hydrogen; an unsubstituted phenyl group, an alkyl group of 1 to 8 carbon atoms; an alkoxy group of 1 to 8 carbon atoms; a nitro group; halogen atoms; a halide; a cyano group; an alkylamino group of 1 to 8 carbon atoms; an aminoalkyl group of 1 to 8 carbon atoms; and a phenyl group having a substitute group selected from an alkyl group of 1 to 8 carbon atoms, an alkoxy group of 1 to 8 carbon atoms, a nitro group, halogen atoms, a halide, an alkylamino group of 1 to 8 carbon atoms, an aminoalkyl group of 1 to 8 carbon atoms and cyano groups, or two neighboring substituents among R1, R2, R3, R4, R5, R6, R7 and R8 are fused and substituted with 1 to 3 aromatic cyclic compounds having formula (2a) through (2g), and unsubstituted groups among R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from the group consisting of hydrogen, an alkyl group of 1 to 8 carbon atoms, an alkoxy group of 1 to 8 carbon atoms, an allyl group, halogen atoms, a halide, a cyano group and a nitro group;
M is metal ions with an oxidation number of 2 capable of being complexed with the tetrazaporphyrine ring, or metal ions having ligands with an oxidation number of 2 capable of being complexed with the tetrazaporphyrine rings 
where Rxe2x80x2, Rxe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x3xe2x80x3xe2x80x2 are independently selected from the group consisting of hydrogen, an alkyl group of 1 to 8 carbon atoms, an alkoxy group of 1 to 8 carbon atoms, an allyl group, a cyano group and a nitro group; X is halogen atoms or alkyl sulfonate of 1 to 8 carbon atoms; Y is an alkyl or allyl group of 1 to 8 carbon atoms; and dashed lines indicate a portion coupled with the pyrrole group of formula (3).
The second object of the present invention is achieved by a selectively light-absorptive coating composition comprising the light-absorptive material, a plastic resin and an organic solvent.
The third object of the present invention is achieved by a selectively light-absorptive filter for a color display, formed of the selectively light-absorbing material and a plastic resin.